Terephthalic acid is one of the largest commodity chemicals manufactured worldwide with production estimated at 8.49 billion pounds yearly (See Kirschner M., PTA/DMT, Chemical Market Reporter 2004 Nov. 22-29; 266(18):31). Terephthalic acid is used as a starting material monomer in the production of a wide range of polyethylene terephthalates, from soil release polymers for use in laundry detergents (U.S. Pat. No. 4,702,857) to the manufacture of plastic bottles and containers.
Terephthalic acid is typically manufactured by the air oxidation of 1,4-dimethyl-benzene (para-xylene) in acetic acid employing a cobalt molybdenum catalyst. Because the reaction does not result in 100% conversion, impurities are usually present, most notably 4-carboxybenzaldehyde (4-CBA). However, in order to use terephthalic acid as a starting material, for example, for the preparation of polyethylene terephthalate copolymers, terephthalic acid must be very pure.
One commercial process for the purification of terephthalic acid involves dissolving the impure terephthalic acid in water at a temperature of about 300° C. where the solubility of terephthalic acid is about 40%. At this point, most of the 4-CBA is removed and the terephthalic acid is crystallized through a series of 5-6 crystallizers, which operate at sequentially lower temperatures and pressures.
In order to purify the crude terephthalic acid by such methods, large quantities of energy and water are necessary. Indeed, recovery of the large quantities of water that are rendered unusable during the purification of terephthalic acid has itself been the subject of much research. (See Kleerebezem R et al., High rate treatment of terephthalic acid production wastewater in a two-stage anaerobic bioreactor, Biotechnol. Bioeng. 2005 Jul. 20; 91(2):169-79; and Thiruvenkatachari R. et al., Degradation of Phthalic Acids and Benzoic Acid from Terephthalic Acid Wastewater by Advanced Oxidation Processes, J. Enviro. Sci. and Health Part A: Toxic/Hazardous Substances & Environmental Engineering, 2006; 41(8), 1685-1697.)
There is, therefore, a long felt need for a low temperature and low water volume process for purifying terephthalic acid. The compositions, methods and devices disclosed herein meet these and other needs.